Many modern wireless handheld communications devices, whether cellular telephone handsets or personal digital assistants (PDAs) are equipped with ancillary features.
One such feature that is gaining popularity is a Global Positioning System (GPS) receiver, whereby the present location of the handset or PDA may be established to within a precision of a few to a few hundred feet and by which a precise map of the immediate vicinity and/or directions from such present location to a desired destination may be provided.
A GPS receiver clock circuit typically uses a crystal oscillator (XO) or temperature compensated crystal oscillator (TCXO) to generate its local clock. These crystal oscillator or TCXO output signals, even with temperature compensation, are subject to variations due to changes in temperature, which may occur as the GPS receiver is moved to different locations, environments and temperatures, or when internal circuits generate heat. The oscillator signal variation in frequency in response to temperature change is complex and not necessarily uniform.